Intercommunicating teletypewriter system



March 29, 1949. w. M. BACON INTERCOMMUNICATING TELETYPEWRITER SYSTEM 2 Sheets-Sheet 1 Filed Jan. 16, 1945 @Sku o d SGL met.

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W M BACON JWM ATTORNEY March 29, 1949.

W M. BACON INTERCOMMUNICATING TELETYPWRITER SYSTEM 2 Sheets-Sheet 2 Filed Jan. 16, 1945 Y NMA MNE - Arrow/Ey Patented Mar. 29, 1949 UNITED STATES PATENT OFFICE INTERCOMMUNICATING TELETYPEWRITER SYSTEM Walter M. Bacon, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated,

20 Claims.

This invention relates to intercommum'cating teletypewriter systems, and more particularly to automatic testing and alarm circuits for use therewith.

An object of the invention is to indicate to an attendant at one of a plurality of interconnecting stations, by means of visual and/or audible alarm, Whenever the systems -condition of operation is such that the system fails to function in a satisfactory manner for one or another of a, variety of reasons in which case a circuit is not assured.

According to an exemplary and preferred embodiment of the invention, an intercommunicating teletypewriter system is equipped with testing facilities automatically operable whenever (l) the line circuit interconnecting two stations and normally energized is conditioned for operation and (2) transmission of message signals is discontinued and the channel or transmission line does not restore to its normal, idle condition. The testing facilities are not a part of the normally energized line but are controlled by certain signals which are automatically transmitted over the line at regularly recurring intervals of time. The testing facilities include alarm equipments which are automatically operated whenever the line remains open or closed for a prolonged interval.

Among the features of the present invention are the provision of equipment for automatically indicating by visual and audible alarm signals either during the transmission of a message or when the circuit is idle whenever 1) there is a failure of the line between stations due to the line remaining open or locking closed for a prolonged interval of time, (2) there is a failure of the sending machine to send signals to the line, (3) there is a failure of the receiving machine to respond to signals incoming over the line and (4) there is primary power failure at either or both the sending and the receiving machines.

Among other features are the provisions for (l) transmitting selected non-message signals or impulses such as letters signals at regular intervals to the remote station during idle periods to furnish at both stations information with respect to the usable condition of the line interconnecting the stations, (2) indicating to the attendant at the receiving station that the message signals transmitted over the interconnecting line circuit are not being recorded at the remote station for a period in excess of another given interval of time, (3) preventing the operation of the tape-feed mechanism of the automatic tape transmitter at the sending station when the letters signals are being transmitted to the remote station at regular intervals during the idle periods, and (4) providing an automatic non-interfering tape feed-out at the end of each message if required.

In the normal operation of the exemplary embodiment of the invention disclosed as applied to a one-way channel, the probability of the loss ci messages is greatly reduced because a continued marking condition of the line for more than the assigned time of about seven seconds (other shorter or longer times may be used) or a continued spacing condition of the line for more than an assigned time of one-half second or more; or a failure to receive periodic check signals causes an alarm to be sounded or registered at the receiving terminal and attending personnel will recognize such alarm and take steps to correct the abnormal condition. In the case of a two-Way system on separate lines, information of the abnormal condition may be transmttcd beck to the opposite terminal to prevent further attempts at transmission until the condition has been corrected; in the case of a duplex line or two-way wires in single cable or upon a single pole line, the abnormal condition may or may not be present upon both channels of transmission depending upon its source or cause.

Apparatus embodying the invention may be utilized with a one-way channel or with each direction of transmission upon a duplex channel. Although the exemplary embodiment is disclosed in detail as a two-wire duplex channel in which each wire carries transmission in one direction only, known methods of consolidating the two wires into a single wireduplex channel are available and can be employed for the purpose by any one having an elementary knowledge of duplex telegraphy; likewise the application of the invention to systems including radio or carrier current links are considered to be comprised within the disclosure because methods of converting'two line conditions to two carrier wave conditions and vice versa for modulated or interrupted carrier Wave transmission are also Well known to those havng an elementary knowledge of the art.

This invention will be better understood from the following detailed description of an exemplary embodiment when read in connection with the accompanying drawings wherein:

Figs. 1 and 2 represent an intercommunicating teletypewriter system designed for full duplex operation. Fig. l shows station A and 2 shows station B, the stations being interconnected by two normally closed single line circuits for respectively transmitting in opposite directions. Each line circuit, channel or path may be equipped at one or more intermediate points w-th quipment |08 which typliies any or all types of repeaters, electromagnetic, thermonic or regenerative as well as carrier links or radio links, composite legs or any of several of these or other equipment normally used in or as part of a telegraphic transmission path; however, the principles of the invention are applicable to a direct unrepeatered transmission channel although such application of them may not develop the maximum utility of the invention.

Referring to Fig. 1, station A comprises, (1) for sending, keyboard perforator for perforating tape |0|, an automatic tape transmitter |02 for translating outgoing message signal combinations on perforated tape |0| into coded signal current combinations for transmission over five segments of start-stop rotary distributor |03 to conductor |04 of the normally closed line circuit extending to station B, keyboard transmitter and printing unit |05, which may be substituted at any time, by means of switch |06, for the automatic tape transmitter |0| for transmitting coded signal current combinations directly to the line conductor |04 and a single line regenerative repeater |08 shown in diagrammatic form and representing one or more repeaters in the line conductor |04, and, (2) for receiving, a diagrammatic showing represented by rectangle |01, of a typing reperforator or other type of teletypewriter for receiving coded signal current combinations over the other line conductor 203 from station B and the necessary test and alarm equipment which functions with the receiving equipment of the system. Rectangle |01 represents equipment similar to the receiving equipment shown in detail in Fig. 2.

Referring to Fig. 2, station B also comprises, (1) for sending, a keyboard perforator and a tape perforated thereby, an automatic tape transmitter, a start-stop rotary distributor and a keyboard transmitter represented diagrammatically by block 20|, and one or more single line regenerative repeaters represented by block 202, line conductor 203, and (2) for receiving purposes a typing reperforator 204 or other type of teletypewriter for receiving coded signal current combinations over line conductor |04 from station A and the testing and alarm equipment required for said incoming coded signalcurrent combinations.

The machine transmission means comprises an automatic tape transmitter and rotary distributor at each station combined in a device identified as the transmitter-distributor set |09, a description of which may be had by reference to U. S. Patent 2,262,014 granted toW. Y. Lang on November 11, 1941. The typing reperforators |01 and 204 at stations A and B, respectively, are of the type disclosed in C. W. Swan, U. S. Patent 2,308,554, issued January 19, 1943.

In Fig. 1 the transmitter is provided with the usual tape feed mechanism (not shown) and tape feed withhold mechanism (not shown) operated or controlled by tape feed withhold magnet |52. Tape feed withhold mechanism of suitable nature is known to workers in the art. One form of tape feed mechanism comprises a pawl and ratchet operated mechanically on each revolution of the distributor after the sensing pins have been withdrawn from the tape to advance the tape to bring forward a new code combination for sensing. The tape feed withhold magnet, when energized, lifts the pawl from the ratchet so that the pawl operates idly. Such devices are sumciently well known to need no description but nevertheless a disclosure may be found in Fig. 6 of the application of Bacon, Serial No. 371,521, filed December 24, 1940, magnet |52 hereof corresponds to magnet 61| of said application, the disclosure of said mechanism is incorporated herein by reference to the same extent as if set forth in full.

Perforated tape |0| may be fed from a keyboard operated perforator |00 or from a reperforator (not shown) operated under control of a line (not shown) incoming at station A or it may be supplied manually with pieces of tape perforated with messages to be sent. Usually, however, tape |0| will extend from a perforator or a reperiorator directly to the sensing head of the transmitter and the tape-stop arm ||0 will stop transmitter-distributor |09 when the tape becomes taut due to the cessation of perforator |00. Correponding elements of station B are arranged in a similar manner. The transmitter-distributor at each of stations A and B may be considered to typify any type of machine transmitter including those which have mechanical distributors as well as those which have segmental distributors.

Distributor |03 in its idle condition, connects line conductor |04 to a circuit extending over its inner ring, brushes at its stop segment, conductors ||2 and H3, right-hand normally closed contacts of switch |06, through the upper winding of polarized line relay I|5, to grounded negative battery |41, the opposite end of the circuit of the conductor |04 extending through an intermediate single line repeater |08, through the upper winding of polarized relay 2F, through the upper winding of polarized relay 205 of the typing reperforator 204, to grounded positive battery 203. Line relay ||5 is thereby normally held in its marking or left-hand position as shown to hold printer magnet ||6 operated when no messages are being transmitted. Relay 2-F is normally held in its marking, or righthand, position, as shown, to normally hold slowto-release relay 2-G operated. Relay 205 is normally held in its marking or right-hand position, as shown to hold the reperforator printing magnet 206 operated. Relay 2-B at station B is also normally held in its operated position by universal contacts 201 of reperforator 204, in their normally closed position. When current switch |5| is operated to its closed position stop magnet |-SM operates in a circuit traceable to ground at the back contact and upper armature of relay |-C. Tape feed withhold magnet |52 is also operated when current switch |5| is closed, and thereby preventstape |0| from advancing during the idle periods, that is, when no messages are being transmitted. Tape |0| is not advanced when the circuit assurance letters signals are being transmitted every seven seconds during the idle periods or when letters signals for accomplishing tape feed-out at the receiving station are being transmitted thereto. All other equipment during idle periods of the system is in its normally deenergized condition.

Method of operation When the system is in its idle condition letters signals are continuously repeated from station A to station B over line conductor |04 and from station B to station A over line conductor 203 at given intervals, say seven seconds, to give the operator at each end of the system assurance that his incoming transmission line, his receiving machine and the transmitting machine at the remote terminus oi the channel are in operative condition. For the purpose of illustration, it will be hereinafter assumed that station A is sending and station B is receiving and only that equipment which is shown in de tail at stations A and B will be described under the method of operation.

Station A During the idle period, it will be assumed that power switch and battery switches |20 and l5! are in their respective closed, or operated, positions, and message transmission start switch |22 is open. It will also be assumed that automatic transmitter-keyboard switch |98 is in the position shown so that the automatic tape transmitter |09 is operatively connected to line conductor |06 and the keyboard i i4 is shortcircuited. Motor H8 is normally operating and stop magnet i-SM is energized so that the brushes on distributor |23 are operating to send feed-out signals to the line until the timing intervals begin.

At the time battery switch |5| was operated to its closed position (l) the operating circuit for stop magnet l-SM was established to cause`the magnet to operate and thereby permit the rotation of the brushes of distributor |63 and (2) the operating circuit for withold magnet |52 was established to operate magnet |52 whereby the tape feed mechanism of automatic transmitter i was prevented from operating during idle periods, whereby repeated letters signals are sent to the line as will now be described. When battery switch |23 was operated it closed at its lower contacts an energizing circuit for the lament of vacuum tube |2| and at its upper contacts an operating circuit for relay |-E and relay i-E operates. Relay |E, upon operating, opens a shunt path around condenser |26 which immediately begins to charge to a potential suflcient to render Vacuum tube 2| conductive, the circuit being traceable from grounded negative battery |2'i, lower contacts of switch |2, resistance |28, condenser |26, conductors |29 and |39, outer lower armature and back Contact of relay l-C, conductor |3|, resistance |32, conductor |33, resistance |34, grounded positive battery |35. Condenser |23 accumulates a sufficient charge to make vacuum tube |2| conductive and relay I-A therefore operates. During this charging time repeated letters signals will be sent from the transmitter and cause the tape the receiving station to feed out for about four seconds.

Relay |-A, upon operating, closes at its armature and Contact, an operating circuit for relay i-B which operates. Relay l-B, upon operating, (l) opens at its upper armature and back contact the operating circuit for relay l-E which now releases, (2) closes at its upper armature l and front contact a substitute operating circuit for stop-magnet |-SM, the circuit referred to hereinafter as the rst substitute operating circuit, being traceable from ground, upper armature and iront contact of relay |-B, conductor |36, left-hand normally closed contact of switch |06, conductor |31, through the winding of stop-magnet i-SM, resistance i38, to grounded negative battery |39 and the magnet |-SM is held operated after relay i-C operates, prior to the recurring intervals of seven seconds duration .used fori the transmissionpof 6 test letters signals, as will be hereinafter described, (3) closes at its inner lower armature and front contact a circuit traceable from ground, conductor |49, through the winding of relay l-C,

to grounded negative battery and relay |-C opcrates to open the original operating circuit for stop-magnet l-SM and (4) closes at its outer lower armature and front contact an operating circuit for message register magnet i--MR which operates to furnish a visible record of the number of seven second intervals that occur during the idle periods of the transmission line tdt. Relay l-C, upon operating, (l) as hereinbefore stated, opens at its upper armature and contact the original operating circuit for stop-magnet i SM, (2) closes at its inner lower armature and contact a locking circuit for itself which extends over the back contact and No. 2 armature of relay l-D to ground and (3) opens at its outer lower armature and contact a shunt path around resistance Mi which has .a comparatively high resistance value. The locking circuit for relay i-C is maintained for the duration of an idle period, that is, until message transmission begins. The letters signal combination representing the test signals transmitted at seven second intervals comprises a start, or open, impulse, five closed, or current, impulses and a stop, or closed, impulse. For each character signal, the start, or open, impulse is transmitted over the unconnected start segment of distributor |93 to line me; the next live impulses which are known as the selecting impulses are transmitted from grounded negative battery till, over either of two paths, one including conductors H3, M3 and |49 and the normally closed contacts of automatic tape transmitter |02 and the other path, including conductors ||3 and H2, and any of the normally open contacts of transmitter |532, which happen at this time to be closed because of tape perforations appearing over transmitting, or sensing, pins or transmitter |22, then over segments Nos. l to 5, in turn, of distributor |93 to line mit; and the stop, or closed, impulse is transmitted over conductors H3, ||2 and Hi and the stop segment. It will be noted that when there is no perforated tape in transmitter |62 or when there are no tape perforations over the transmitting, or sensing, pins, the iirst-mentioned path short-circuits the second-mentioned path which includes the normally open contacts of transmitter 22 Relay i-E, upon releasing, causes condenser |26 to discharge through resistance M2, vacuum tube |2| to become non-conductive and relay l-A to release. The release or" relay i-A effects the release of relay |-B. Relay l-B, upon releasing, (l) opens the operating circuit for message register magnet |-MR which releases, (2) opens the original operating circuit for relay |-C and (3) opens the substitute operating circuit for stop magnet I-SM which now releases and (4) recloses the operating circuit for relay i-E which again operates. Inasmuch as relay E-C at this time is locked in its operated position to mainn tain open the original operating circuit for stop magnet l--SM and the substitute operating circuit for stop magnet l-SM is also opened at the front contact and upper armature of relay I-B now released, stop magnet i-SM now releases and its armature arm |43 is moved into engagement with cam |44. Cam |44, when so engaged, stops at the end of one revolution the rotation of the brushes of distributor |03.

Relays I-E, upon operating the' second time,

causes condenser |26 to recharge. The recharging circuit, because of relay I-C being locked in its operated position, includes resistance |4| whose value is such, together with condenser |26, as 'to cause the letters signals to be transmitted at regular recurring intervals each having a definite duration of seven seconds. After each interval of seven seconds vacuum tube |2| becomes conductive, as before, to momentarily operate relays |-A and I-B, in turn. Each time that relay |-B operates during an idle period stop magnet I--SM operates to release distributor shaft |46 which upon rotating the distributor brushes causes to be transmitted over conductor |04 to station B a letters signal. Relay |B, upon releasing the second time, opens the operating circuit for stop magnet l-SM which again releases to cause the rotating brushes of distributor |03, upon reaching their stop segment, to come to rest until the eXpiratlon of another seven second interval. When vacuum tube |2| again becomes conductive, relays |A and I-B again operate, in turn. These cycles are repeated continuously during an idle period of conductor |04.

Station B At a transmission rate of sixty words a minute each complete character code combination requires about one-sixth of a second for transmission. As each letters signal is received in the upper winding of polarized relay Z-F at station B, the relay armature during the space, or open, impulse received as a start impulse, moves from its normally closed or marking contact to open the operating circuit of relay Z-G, but relay 2-G which is of the slow-to-releasel type does not respond to the start impulse of a letters signal, or any other permutation code signal. Relay 2-G may be of a type timed to release in anything from about one-half second to several seconds and typifying any sutable timing device for timing such a period. However, .the typing reperforator 204 operates in response to each incoming letters, that is, each of the entire signal combina-` tions including the start, or space, impulse and th-e stop or mark, impulse to furnish the operator at station B with the information that the letters signals are being reecived and that the line circuit including conductor |04 as well as the sending transmitter-distributor and the receiving reperforator is capable of operation. Should a break or continued spacing condition occur in the line circuit of conductor |04, then relay 2--F would remain in its left-hand, or spacing, position for the duration of the sustained open, or break, condition in the line and therefore relay 2-G would release. Relay 2-G, upon releasing, (l) opens at its outer upper armature and contact its normally closed holding circuit, (2) closes at its inner upper armature and contact the buzzer circuit which extends from the negative pole of the separate local battery 209, conductors 2|0 and 2||, inner upper armature and contact of relay 2--G, conductor 2|2, normally closed contact of switch 2|3, conductor 2|4, through the winding of buzzer 2|5, to the positive pole of battery 209 and the buzzer starts operating to furnish an audible alarm to indicate the open condition of line |04, and (3) closes at its lower armature and contact a circuit for lighting the break and open lamp 2|6 Which lights to furnish a visual alarm if the line circuit of conductor |04 is open. Lamp 2|6 and buzzer 2|5 will continue to furnish the desired alarms until switch 8 2| is operated which, upon being operated, closes at its upper contact a substitute operating circuit for relay Z-G which operates to extinguish lamp 2|6 and stop buzzer 2 5.

Transmission from station A to station B In order to start message transmission from station A to station B, it is rst necessary to establish What is called herein the normal idle condition (as distinguished from the out-of-service condition) by moving power switch and battery switches and |5| into their operated positions, and to determine whether the transmission is to be performed through the automatic tape transmitter |09 or the keyboard transmitter |05. Assuming that transmission is to be with automatic transmitter |09, the automatic transmitter-keyboard transmitter switch |06 is in the position shown, perforated tape is placed in the transmitter and then message transmission start switch |22 is operated to its closed position. The closure of start switch |22 closes a circuit from ground through the normally closed sixth pin contacts |24, which are closed when tape is in the transmitter, switch |22, through the upper winding of relay |-D, to grounded battery and relay l-D operates and (l) locks in a circuit traceable from grounded battery, through its lower winding, front contact and armature No. 7, tape stop or taut tape contacts |23, contacts |24, to ground, (2) opens at its No. 1 armature and back contact the circuit for short-circuiting the transmitter contacts, (3) opens at its No. 6 armature and back contact the operating circuit for relay l-E which releases at this time to prevent rst, the charging of condenser |26 and second, the repeated operation and release of relays |A and I-B for sending the circuit assurance letters signal, (4) opens at its No.5

armature and back contact the operating circuit for tape feed withholding magnet |52 which now releases whereby the tape feed mechanism becomes free to operate, (5) opens at its No. 2 armature and back contact the locking circuit for relay |-C which now releases inasmuch as relay |-B is also released, (6) opens at its No. 3 armature and back contact the original operating path for stop magnet |-SM, (7) closes at its No. 4 armature and front contact a sustained operating path for stop magnet l-SM which now reoperates to start transmission on message signals. With perforated tape available the message is transmitted because stop magnet I-SM is held operated. The non-operation of tape feed withhold magnet at this time permits the tape feed mechanism to feed tape so long as a supply is maintained by operation of the keyboard perforator |00.

Should transmission by the distributor |03 use all perforated tape |0l, the perforated tape |0| would reach a predetermined minimum, whereupon tape |0| would become taut to actuate tape stop arm ||0 in an upward direction to open the taut tape contacts |23 thereby opening the second substitute operating circuit for stop magnet I-SM, the second substitute operating circuit being different from the corresponding first substitute operating circuit for stop magnet |-SM which is applied during normal idle condition. The second substitute operating circuit for stop magnet l-SM is traceable from grounded battery |39, battery switch |5I, resistance |38, winding of stop magnet |-SM, conductor |31, lefthand closed contacts of switch |00, No. 4 armature and front contact of relay |`D, conductors 9 |53 and |54, and contacts |23 and |24 to ground. The opening of the second substitute operating circuit for stop magnet I-SM at taut tape contacts |23 causes the release of stop magnet l--SM thereby stopping the rotating brushes of distributor |03, and transmission ceases until suficient additional tape is perforated at keyboard perforator |00 to permit tape stop arm H0 t0 drop into its normal position and thereby again close contacts |23. During this interval wherein the rotatable brushes on distributor |03 are in their stop position marking current will continue to be connected to line conductor |04 until the supply of prepared tape l0! becomes sucient to close contact |03 to resume transmission. Relay |-D remains operated during the interval wherein there is no supply of perforated tape providing that the start switch |22 is closed.

A portion of the message previously prepared is held up in the taut tape between the tape perforator |00 and the automatic tape transmitter |02. Normally, if the operator discontinues the production of perforated tape the transmission oi signals held in the tape between the perforator |00 and automatic tape transmitter |02 will be delayed until the operation of the tape perforator |00 is again resumed. Il' the operator, upon ceasing to perforate intelligence. or message signals in the tape, perforates sulcient letters blanks or other signals on the tape to advance the end of the last message through the transmitter-distributor. and then opens the transmission start switch 22. relay |-D releases. because the taut tape contacts |23 would also become opened. Upon the release of relay |-D, magnet l-SM is energized and tape withhold magnet |52 is energized; further letters signals are transmitted by rotation of the arm of distributor |03 for four seconds without advancing the tape through the distributor; these letters signals step the tape at the receiving end out of the reperforator (or any equivalent receiving device) so that the message may be torn oil or conveniently read. Relay |-D upon releasing at this time, (1) closes at its No. 6 armature and back contact, the operating circuit for relay I-E which now operates to permit the condenser |26 to start charging to stop the continuous transmission of letters signals to station B. The cessation of letters signals occurs when condenser |26 charges, relay i-A operates, relay l-B operates, relay l-C operates and locks and nally relay |-B releases. (2) Relay |D, in releasing, also closes at its No. 3 armature and back contact the original operating circuit for stop magnet I-SM, which operating circuit extends to the back contact and upper armature of relay l-C. Condenser |26, upon charging for the rst time at the beginning of an idle period, is charged in about 4 seconds in that the charging circuit extends over the outer lower armature and back contact of relay I-C. However, on the next subsequent charging of condenser |26 relay l-C is operated and locked in its operated position so that the charging circuit now includes resistance E 4| and the recurring intervals for charging condenser |26 are uniformly timed at seven seconds each for sending the letters signal to station B during the idle period.

Other alarms If for any reason the line circuit including conductor |04 remains continuously closed so that station B receives a mark signal for a prolonged intervalof time, a universal contact lset 201 in the typing reperforator 204 would furnish an alarm indicating such a condition. The` usual univer-sal contacts of the typingreperforator 204 are controlled to close upon .any selection of the selective mechanismand may be such as shown in Fig. 96 of the drawing of the copending patent application of W. M. Bacon, F. S. Kinkeadand J. A. Krecek, Serial No. 383,490, iiled March 15, 1941, which has matured into Patent 2,381,871 granted August 14, 1945. These contacts, therefore, operate once for each character received.

As hereinbefore stated, if for any reason the line circuit comprising conductor |04 becomes marking and remains so for an interval exceeding thirteen seconds,- a vacuum tube condenserresistance trning circuit would operate to sound an alarm, the principal apparatusso involved being vacuum tube 2.|`8, condenser. 220, and resistance 22|. Accordingly, universal contacts 201 of typing reperforator 204 must operate to their normally open,.or left-hand, position at least once every thirteen seconds, this predetermined time intervalbeing required to operate vacuum tube 2|8 whereby the alarm would operate. During the idle period` of the system reperforator204responds to the incoming letters signal every seven seconds as hereinbefore described and battery switch 2|9 is in its operated. or alternate, position for energizing vacuum tube 218 and charging condenser 220. Ordinarily, when the-universalcontacts 20T are operating to their alternate position in their regular routine duringboth the idle and the transmission periods of the system, a potential of partial value is alternately stored and discharged in condenser 220. as universal contacts operate between their normal and alternate positions and no alarm is sounded. However, if. for any reason the line circuit ofconductor |04 remains marking for a period exceeding thirteen seconds the poential of condenser 220-attains avaiue suiiicient to make vacuum tube 2I8 adequatelyconducting and relay 2K operates. i The charging circuit for condenser. v220 is traceable from grounded positive battery 222, resistance 223, upper contacts of switch 2|9, resistance 22|, condenser 220. resistance 224. to grounded negative battery 225. and the discharging circuit is traceable frorn grounded battery-225,v resistance 224, condenser 220. conductor 226, universal contacts 20'! in their alternate position, to grounded negative battery 221.

Relay 2-K. upon operating, closes at itsarmature and contact an operating circuit from ground. its armature and contact. conductors 228 and 229, through the winding of relay 2L to grounded battery and relay 2-L operates. Relay 2L, upon operating, (1) closes at its upper armature and contact an operating circuit for buzzer 2|5. the circuit being traceable from the negative pole of battery 209. conductor 2| n. contact and u'oner armature of relay 2 1. conductor 2'2. normally closed contacts of .switch 2|3. conductor 2| 5. through the buzzer 2|5. to the positive role of battery 208 and the buzzer o'oerates to furnish an audible alarm. (2) closes at its lower armature and contact a circuit for lighting lamp 230. The lamp 230 lights to furnish a visual alarm. indicating a prolonged marking condition Op the 11'1'1e Should the universal contacts 201' remain for protracted period in their alternate position for env reason such as a failure of the receiving machine nr a motor power Failure slow-'release relay 2-B, which is normallyoperatedwill release and close at its upper armature and contact the operating circuit for relay 2-L which operates to cause buzzer 2|'5 to operate and lamp 230 to light as an alarm condition which remains so long as relay 2-B is released. Switches 2|3 and 2|'| may be operated to stop the alarms.

The sixth pin |25 which normally presses against perforated tape as the tape is advanced step-by-step through transmitter |02 serves, as hereinbefore stated, to control contact set |24. Should for any reason the tape be torn or broken or should it pass out of the transmitter the pressure of the tape on pin |25 would be released and contacts |24 would open to release relay l-D, open the operating circuit for stop magnet |-SM which would release to stop the rotation of the brushes of distributor |04, and cause the closure of the operating circuit of tape feed withhold magnet |52 whereby the magnet operates to stop the tape advancing mechanism. The operation of the sixth pin may indicate the end of a message or the end of transmission when a procedure of placing individual message tapes in the transmitter is followed. Upon operation of pin |25 the contact |`24 is opened, relay |D is released (assuming key |06 to the left) and the sending of letters signals at timed seven second intervals begins.

The operation at the sending station may be summarized as follows for various conditions:

(1) Line in out-of-service condition. Switches and |5| are open, switch |20 open, switch |22 ordinarily open but might be closed.

(2) Line is put into service condition but idle with switch |06 to right or keyboard position; nothing happens on line |04 unless and until the keyboard transmitter ||4 is operated.

(3) Line i-s put into service condition but idle with switch |06 to left or automatic condition. Switches |5| and |20 are closed. switch |22 is onen or opened. Distributor |03 starts sending letters signals, relay |-E operates, condenser |26 charges, relay I--A operates after about 4 seconds. relay I-B operates, relay |-C operates and locks, relay l--B releases (sending of letters signals stops). relay-s I-E operates, after seven seconds relay I-A operates, relay |-B operates. start magnet l-SM i-s energized to transmit one letters signal, relay |-E releases as soon as relay |-B releases and the cycle is repeated.

(4) Condition same as (3) but switch |22 closed. tape in transmitter but taut tape contact |23 open. No signals are transmitted bv the distributor or by the timing mechanism under con- "trnl of tube |2| because relay |-D is operated.

(This is not assumed as a usual starting condition.)

(5) Conditions just the same as (4) except taut tace switch |23 is closed. Transmitterdistributor |09 operates to send signals until switch |23 or switch |24 opens. If switch |23 opens nothing further happens unless or until the operator opens switch |22 or takes some other action. If. however, switch |24 opens. relay I-D releases and a sequence oi events similar to those of condition (3) occurs.

(6) Normal transmission is occurring with switch |06 in the left or automatic transmitter position, switch |22 is closed. Let us assume tape runs out of the transmitter and contact |24 opens. rIhe same events transpire as in condition (5) when switch |24 opens.

(7) Same as (6) but instead of tape running out'of transmitter the taut 'tape contact |23 opens. The operator holds control and nothing happens until more tape is supplied. Under this condition if the operator moves switch |06 to the right or keyboard position, relay l--D remains operated, motor ||8 continues running but the path of start relay l-SM is opened at the left contact of switch |05 and the operator can use the keyboard without interference from the automatic transmitter. By restoring switch |05 to the left the operator may return to automatic transmission and supply more tape from perforator |00. If under this condition the operator opens switch |22, relay I-D releases and letters signals are transmitted for four seconds without advancing tape |0| through the transmitter and thereafter there is sent a letters signal every seven seconds without advancing the tape through the transmitter.

(8) Operator with or without opening switch |22 (opening is normal procedure) opens switches |39 and |20 to close down the station.

The operation of the receiving station under these conditions may be summarized as follows, on the assumption that all switches are closed to put the receiver in service, supply it with power and key 2 3 is closed to buzzer 2 I5.

(1) Under condition (1) an alarm will occur in seven seconds; if out of service nothing happens. y

(2) Receiving station in service and supplied with power; in thirteen seconds an alarm sounds but if operator at station A actuates the keyboard once during each thirteen seconds no alarm sounds.

(3) The typing reperiorator records letters signals for four seconds and then one letters signal every seven seconds.

(4) Buzzer 2|5 sounds an thirteen seconds.

(5) The receiver responds to the message signals and then continues as per 3) (6) The receiver responds to the message signals and then continues as per (5) ("1) Thirteen seconds after taut tape occurs and continues at station A the receiving station B sounds an alarm; if transmission occurs from the keyboard at station A in this period or switch |22 has been opened no alarm will sound.

(8) Alarm sounds within 13 seconds if line remains marking.

(9) Under any condition at the transmitter, if no spacing condition is received for thirteen seconds, an alarm will sound.

(10) Under any condition at the transmitter, if no marking condition is received for somewhat over seven seconds, an alarm will be sounded.

What is claimed is:

alarm at the end of 1. In-an intercommunicating system, a channel of impulse transmission having a sending station connected thereto, sending means including distributor means, a tape and tape controlled sending means at said station capable of impressing permutation code message signals on said channel, a taut tape switch for causing said transmitter to pause in sending, means including said distributor automatically operable a predetermined time after said sending means ceases to impress permutation code message signals upon said channel for a reason other than a pause due to said taut tape switch, to send a permutation code test signal over said channel at regularly recurrent intervals each oflong duration in comparison with the interval of a permutation code message signal until said sending means is con--l trolled to resume impressing permutation code message signals on said channel under control of said tape.

2, In combination, a source of permutation code signals, a selector mechanism responsive to signals received from said source, a contact operable to a closed condition by said selector mechanism upon every selective operation by a signal from said source,` .a condenser having a closed path through which it is, charged, a discharge path for discharging said condenser upon opera tion of said contact to said closed condition, and means arranged to be automatically operated by a charge on said condenser whenever said contact, after a predetermined interval of time, fails to operate to said. closed condition in response to signals received by said selector mechanism from said source.

3. In combination, recording telegraph equipment including a selector, a contact associated with said selector and momentarily operated to a closed condition incident to every selective operation of said selector, a timed system including a relaywhich without closure of said Contact, tends to operate said relay in a definite time, and connections between said system and said contact to retime said system upon each operation of said contact to said closed condition by said selector.

4. A channel of telegraphic transmission comprising a transmitter at one point on the channel for sending signal pulses thereover, a receiver at a remote point upon the channel for receiving said signals, timing means for timing a definite period of time, means under control of said channel and operative by any signal or change ci signal condition thereon to reinitiate timing operation of said timing means at zero time, and an indicating device for giving an indication of absence of any change of signal condition upon the completion of timing of said deiinite'period by said timing means.

5. A channel of transmission having at one terminal means connectable thereto for sending marking and spacing conditions, receiving relay means associated with said channel responsive to changes from one to another of said marking and spacing conditions, means associated with said relay means for measuring definite intervals of time, and alarm means actuated by failure of said receiving relay means to respond to a change from either to the other of said marking and spacing conditions for a time equal to or in excess of one such interval.

6. A telegraph channel of communication, a start-stop rotary distributor, an automatic tape transmitter for controlling said distributor in impressing from a perforated tape permutation code signals on said channel, and means automatically effective t0 send over said channel a permutation code signal at regularly recurring intervals having a duration of at least that of two permutation code signals upon and solely under control oi cessation of transmission from the perforated tape in said automatic tape transmitter.

7. A telegraphic channel of communication, principal transmitter means for sending impulses over said channel, and means including supplemental transmitter means capable of being rendered automatically effective to send periodic line check signals at intervals upon and solely under control of cessation of transmission by said principal transmitter means, and responding means at a point upon said channel remote from said principal transmitter means responsive 'to impulses sent over said line by either .of-said 14l transmitter means in combination with means operative to register a troublecondition upon failure of said responding means to receive signal pulses for a continuous period in excess of the normal interval between said line check signals.

8. In a transmission system, a channel of impulse transmission having two stations connected thereto, one station having sending means capable of impressing permutation code character signals on said channel, the other station having means capable of receiving permutation code character signals transmitted by the sending means at said one of said stations in combination with still other means at said one station operable during idle periods and initiated into operation automatically when said sending means ceases to so impress permutation code character signals upon said channel to send a permutation code non-character test signal at regularly recurring intervals each of prolonged duration in comparison with the interval of a permutation code character signal until said sending means resumes impressing permutation code character signals on said channel, and timing means and alarm means controlled thereby operable during intervals of message transmission Whenever said channel remains continuously in fixed signaling condition for said prolonged interval of time.

9. In an intercommunicating system, a channel of impulse transmission having two stations connected thereto and having sending means capable of impressing permutation code character signals on said channel, said sending means including a tape perforated to represent message signals for transmission over said channel, tape feed mechanism for automatically advancing said perforated tape during message transmission, a timing circuit activated automatically upon discontinuance oi message signal transmission by said sending means for causing to be transmitted at regularly recurring intervals during idle periods a permutation code non-character signal over said one channel, and tape feed withholding means for preventing the operation of said tape feed mechanism during the idle periods when the permutation code non-character signal is being transmitted over said channel at recurring intervals.

10. In an intercommunicating system, a chan nel of impulse transmission having two stations connected thereto and having sending means capable of impressing permutation code character signals on said channel, said sending means including an automatic tape transmitter and a rotary start-stop distributor cooperating therewith for transmitting permutation code signals over said channel, a stop magnet for controlling the operation of said start-stop rotary distributor, a perforated tape for controlling the operation of said automatic tape transmitter, means for maintaining said stop magnet energized during the transmission of permutation code character signals, a plurality of contact sets included in said energizing means, a tape stop arm for opening one of said contact sets when the supply of per forated tape becomes insufficient for further transmission to thereby deenergize said stop magnet and stop the operation of said start-stop distributor until such time as the supply ci perforated tape becomes suflicient for further transmission, and an auxiliary pin in contact with said perforated tape for opening another of said contact sets when said perforated tape is broken orftoinor-the supply of'said perforated tape is f exhausted to cause the continuous stoppage of said sending means and the continuous deenerglzation of said stop magnet.

li. A telegraph system comprising a channel of transmission having associated therewith at separated points sending means capable of impressing permutation code character signals for transmission over said channel and receiving means capable of receiving and recording the permutation code character signals transmitted from said sending means over said channel, a power switch and a message transmission start switch for said sending means, said power switch having means when energized for conditioning said system for operation and said start switch having means when energized for starting message transmission over said channel, automatically operated timing means respectively associated with said sending means and said receiving means, said timing means having different operating time intervals, other sending means automatically operable during the idle periods when said system is conditioned for operation for sending over said channel to said receiving means permutation code non-charactertest signals at recurring intervals of uniform duration under the control of one of said timing means, contact means included in said receiving means operative i in response to each permutation code character signal incoming over said channel, and alarm means controlled by the other of said timing means and responsive when said contact means remains in its normal position for a prolonged interval of time during the intervals between message signal transmission.

l2. An impulse transmission system comprising a plurality of stations, a channel interconnecting said stations, means at one of said stations for` sending permutation code signals over said chan` nel, timing means activated automatically only during the idle periods between the transmission of message code signals for measuring and counting predetermined intervals of time, and means cooperative with said sending means and operable once during each of said intervals for sending over said channel one of said permutation code signals for testing the transmission continuity of said system.

1S. A telegraph transmission system comprising a plurality of stations, a channel interconnecting said stations, tape sensing transmitting means at one of said stations, other means cooperating with said tape transmitting means for sending permutation code signals over said channel, a tape perforated with message signals in permutation code, means for advancing said tape through said tape sensing transmitting means, and means automatically operable when said tape passes out of engagement with said tape advancing means to transmit over said channel independently of said tape transmitting means and said tape advancing means signals consisting exclusively of a predetermined successive number of letters signals.

14. A telegraph transmission system comprising a plurality of stations, a line circuit interconnecting said stations, tape sensing transmit' ting means at one of said stations, other means cooperating with said tape sensing transmitting means for sending permutation code signals of marking and spacing over said line circuit, a perforator means for supplying a tape perforated thereby with message signals in permutation code, means for advancing said perforated tape through said tape transmitting means, means including contacts controlled when -the supply of perforated tape reaches a predetermined minimum for stopping transmission of message signals, means at the other of said stations for measuring a marking and a spacing condition in the line circuit having a duration in excess of predetermined intervals of time, and other means at the other of said stations operable after the expiration of said predetermined intervals commencing immediately following the cessation of transmission of message signals for indicating that no signals are incoming over said line circuit.

15. A telegraph transmission system comprising a plurality of stations, a line circuit interconnecting said stations, means at one of said stations for sending permutation code signal groups over said circuit to the other of said stations, timing means at one of said stations operable only during the idle periods between the transmission of message signals for measuring intervals of time of equal and prolonged duration in comparison with the interval of a permutation code signal, means operable during each of said intervals and cooperating with said sending means for sending over said circuit one of said permutation code signal groups for testing the transmission continuity of said circuit, timing means at said other station for measuring intervals of time each of a duration greater than any one interval measured at said one station, contact closing means at said other station responsive to each incoming permutation signal code group for nullifying the effectiveness of said timing means at said other station when signals are received from said circuit, and an alarm means responsive to the operation of said timing means at said other station when signals fail to be received from said circuit, indicating that the said circuit remains in its normally closed condition for a period at least equal to the duration of an interval measured by said timing means at said other station.

16. A telegraph transmission system comprising a p;urality of stations, a line circuit interconnecting said stations, tape sensing transmitting means at one of said stations, means cooperating with said tape sensing transmitting means for sending permutation code signals over said line circuit, a tape perforator means for supplying tape perforated with message signals in permutation code, other means responsive to each code combination perforated in said tape for advancing said tape through said tape sensing transmitting means, starting means operable to condition said system for transmission of signals, a tape-controlled contact arranged to open when the supply of perforated tape is less than a predetermined minimum, a tape feeler and a contact controlled thereby, circuit means operable when said starting means, said tape-controlled contact and said tape feeler contact are closed for sending message signals o-ver said line circuit, a second circuit means operable when said starting means and said tape feeler contact are closed Aand said tape-controlled contact is open for stopping transmission of message signals to the line circuit but permitting continuance of per-- forating message signals in the tape, a third cirmission of message signals to the line but permitting the transmission of a single permutation code signal to the line circuit at regular recurring intervals of time independently of said tape advancing means.

17. Transmitter means including a tape-controlled transmitter having tape sensing feelers for sensing signal impressed tape at a transmitting point7 a distributor, an outgoing line to which said transmitter means is connected over said distributor, tape advance means associated with said feelers for stepping said tape, a feeler for sensing the presence of tape at said transmitting point, a contact actuated by said feeler upon absence of tape at said transmitting point, means controlled by actuation of said contact to initiate the sending of code combinations to said line over said distributor independently of said tape sensing feeler, and delayed action means for stopping the sending of such code combinations.

18. Transmission means including a tape sensing head having tape sensing code elements, a distributor having start means for transmitting, one at a time, code combinations sensed by said elements, a feeler for detecting the presence of tape in said head and operating a contact when said head becomes void of tape, means operated incident to operation of said contact for setting up on said distributor a definite code combination and energizing said start means to start condition, and delayed action means also set into operation incident to operation of said contact to deenergize said start means and thereby stop said distributor after transmission of a substantial number of said definite code combinations.

19. In combination, a recording telegraph signal receiver including a permutation code responsive selector mechanism operable in cycles individual to each received permutation code signal, a transfer contact means momentarily operable oli-normal by said selector mechanism in each operating cycle thereof, a condenser having a closed charging circuit, a discharge path for said condenser adapted to be completed by said con- 4 tact means during the oir-normal operation thereof, a circuit including an electron discharge 18 device controlled by said condenser, and an alarm device operable by said last-mentioned circuit upon activation of said electron discharge device by said condenser when charged.

20. A telegraphic channel of communication, a start-stop rotary distributor, an automatic transmitter for controlling said distributor in impressing from a perfo-rated tape permutation code signals on said channel, means automatically effective to send over said channel a permutation code signal at regularly recurring intervals each having a duration of at least that of two permutation code signals upon and solely under control of cessation of transmission from the perforated tape in said transmitter, responding means at a point upon said channel remote from said distributor responsiv e to permutation code signals sent over said channel by said transmitter and the rst-mentioned means, and other means operative to register a trouble condition upon failure of said responding means to receive permutation code signals for a continuous period having a duration in excess of the duration of at least that of two permutation code signals.

WALTER M. BACON.

REFERENCES CHTED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,579,999 Benjamin Apr. 6, 1926 1,835,549 Wishard Dec. 8, 1931 1,398,921 Watson Feb 21, 1935 2,160,083 Peterson May 30, 1939 2,214,572 Bernstein Sept. 10, 1940 2,275,940 Backus et al Mar. 10, 1942 2,293,704 Blanton Aug. 25, 1942 2,296,845 Goetz Sept. 29, 1942 2,331,914 Janiszewski Oct. 19, 1943 2,370,445 Brown Feb. 27, 1945 2,376,11 Bacon May 15, 1945 FOREIGN PATENTS Number Country Date 207,418 Switzerland 1940 

